Background. The physical activity transition is contributing to an increase in childhood obesity and a decrease in fitness worldwide. This study compared body composition and fitness measures in children from three countries and examined intercountry differences in the relationship between these variables. Methods. Participants consisted of 736 Canadian, 193 Mexican, and 179 Kenyan children aged 9-13 years. Body mass index (BMI), waist circumference, triceps skinfolds, aerobic fitness, and muscular fitness were measured. Linear regression was used to examine associations between variables. Results. The prevalence of obesity was the highest in Mexican children (9.2% boys, 8.4% girls) and the lowest in Kenyan children (0.9% boys, 2.8% girls). Aerobic fitness (VO2max in mL/kg/min) was the highest in Kenyan children (50.2 boys, 46.7 girls) and the lowest in Canadian children (41.3 boys, 38.3 girls). Aerobic fitness was negatively associated with body composition measures irrespective of country and sex. Mexican children with low aerobic fitness had higher body composition measures than Canadian and Kenyan children. Muscular fitness was not associated with the body composition measures in Kenyan children but was a weak positive correlate of BMI and waist circumference in Canadian and Mexican children. Conclusion. The current study provides some evidence to support the physical activity transition hypothesis.
This study investigated associations between screen-use (time and type) and cognition in children and tested the hypothesis that across all screen types, time spent on screens is negatively associated with cognition. Methods This study presents cross-sectional data from 11,875 US children aged 9–10 years. Exposures were self-reported daily recreational screen-use. The primary outcome was global cognition measured by the Youth NIH Toolbox®. Covariates included child education, pubertal development, parental education, household income, race/ethnicity, physical activity, and sleep duration. Findings The mean (SD) daily recreational screen time was 3.8 (3.1) hours and 99.7% of children reported using some form of screen daily. More screen time was accumulated on weekends compared to weekdays [4.6 (3.6) vs. 3.5 (3.1) hours, d = 0.34, p < 0.001], and boys reported more screen time than girls [4.1 (3.1) vs. 3.4 (3.0) hours, d = 0.22, p < 0.001]. Children in the high (7.2 h/day; β = −1.76 [-2.12, −1.40]) and middle (2.9 h/day; β = −0.82 [-1.15, −0.48]) daily screen time tertiles had lower measures of cognition compared to children in the low tertile (1.2 h/day). Children in the high tertile for TV watching (2.5 h/day; β = −0.99 [-1.55, −0.64]), video watching (2.3 h/day; β = −1.05 [-1.43, −0.67]), and social media (1.4 h/day; β = −0.79 [-1.14, −0.44]) had lower measures of cognition compared to children in the low tertile for each variable (0.3 h/day, 0.1 h/day, and 0.0 h/day, respectively). Higher video game time was positively associated with cognition compared to the low tertile (β = 0.12 [-0.25, 0.48], p = 0.53). Conclusions Higher daily screen time is associated with lower cognition in children. These findings suggest moderating screen-use for promoting cognitive development in children.
Meeting 24-h movement guidelines by children and adolescents has been associated with improved indicators of health, although it has been under-studied in China. Hence, this study aimed to investigate the prevalence of meeting the 24-h movement guidelines, its correlates, and its relationships with body mass index in children and adolescents in China.
Recent concerns over the risks of hormone replacement therapy in postmenopausal women have increased interest in assessing alternative therapies to preserve the health and well-being of women as they age. Because of the dramatic changes observed in the endocrine system as women age, particularly with anabolic hormones, there is interest in the potential for exercise to promote a hormonal milieu that preserves or enhances physiological function, especially muscle and bone mass, and healthy aging. To examine this potential, the papers from this symposium assessed different but related areas of exercise endocrinology in women. The symposium addressed important work on energy balance and reproductive function, exercise and estrogen interactions on health in postmenopausal women, and how age affects hormonal responses to exercise in women. Methodological inconsistencies make it difficult to draw definitive conclusions, which highlights the need for additional, carefully controlled work in this area. Key words: hormones, physical activity, female, methodological issues